1. Field of the Invention
The present invention relates to a rotary drum apparatus and, in particular, to a rotary drum apparatus having a high precision head rotation locus.
2. Description of Related Art
A conventional video tape recorder records and/or reproduces predetermined video signals using a rotating magnetic head mounted on a rotary drum apparatus. The magnetic head forms recording tracks on a magnetic tape wound around the rotary drum apparatus. The recording tracks are formed on the magnetic tape sequentially and helically in relation to the longitudinal running direction of the magnetic tape.
FIGS. 1 and 2 illustrate a conventional central rotary drum apparatus 1 having a central rotary drum 11 that rotates between a cylindrical fixed upper drum 3 and a cylindrical fixed lower drum 4. The fixed upper drum 3 is connected to a support material 2 with screws 7A and 7B, and the cylindrical fixed lower drum 4 is connected to the support material 2 with screws 8A and 8B.
The central rotary drum 11 is supported in free rotation between the fixed upper drum 3 and fixed lower drum 4. A magnetic head 12 is fixed to the central rotary drum 11 projecting slightly from the outer circumference of the central rotary drum 11. The central rotary drum 11 is rotated by a drive motor 6 and, according to this rotation, the magnetic head 12 rotates between the fixed upper drum 3 and the fixed lower drum 4.
A magnetic tape (not shown) runs helically on the rotation locus of the magnetic head 12 fixed on the central rotary drum 11 along the outer circumference of the fixed upper drum 3 and fixed lower drum 4. The rotating magnetic head 12 can sequentially and helically form recording tracks in the longitudinal direction on the magnetic tape.
FIG. 3 is a sectional view of the conventional rotary drum apparatus 1 of FIGS. 1 and 2. As seen in this figure, a transformer frame 4A is formed at a lower side of the fixed lower drum 4, and a stator 13A of a rotary transformer 13 is fixed in the transformer frame 4A. In addition, a cylindrical bearing holder 4B is formed through the transformer frame 4A, and a rotary shaft 14 is supported in free rotation through bearings 15A and 15B held within the bearing holder 4B.
A flange 16 is engaged to the rotary shaft 14, and a rotor 13B of the rotary transformer 13 is fixed to a lower side of the flange 16. The central rotary drum 11 is fixed to an upper side of the flange 16. Thus, as a drive motor 6 mounted at a lower edge of the rotary shaft 14 rotates the rotary shaft 14, the rotor 13B of the rotary transformer 13 and the central rotary drum 11 are rotated.
A head base plate 21 is fastened on the outer circumference of the central rotary drum 11. The magnetic head 12 is fixed to the central rotary drum 11 through the head base plate 21. The height of the magnetic head 12 can be finely adjusted with an adjustment screw 22.
Thus, this rotary drum apparatus can record and/or reproduce predetermined video signals on the magnetic tape (not shown) by contacting the outer circumference of the magnetic head through an arrangement to make the magnetic head 12 project outside from the gap between the fixed upper drum 3 and the fixed lower drum 4.
Another conventional drum apparatus 30 is shown in side view in FIG. 4. This apparatus includes an upper rotary drum 33 rotatably mounted on a fixed lower drum 4. The upper rotary drum 33 is supported on the fixed lower drum 4 in free rotation. The magnetic head 12 is fixed to the upper rotary drum 33 and projects slightly from the outer circumference of the upper rotary drum 33. As the upper rotary drum 33 is rotated with a drive motor 6, the magnetic head 12 rotates firmly with the upper rotary drum 33.
A magnetic tape (not shown) runs helically on the rotation locus of the magnetic head 12 fixed on the upper rotary drum 33 along the outer circumference of the upper rotary drum 33 and the fixed lower drum 4. The rotating magnetic head 12 can sequentially and helically form recording tracks in the longitudinal direction on the magnetic tape.
FIG. 5 shows a sectional view of the rotary drum apparatus 30 of FIG. 4. As seen in this figure, a transformer frame 4A is formed at a lower side of the fixed lower drum 4, and a stator 13A of a rotary transformer 13 is fixed in the transformer frame 4A. In addition, a cylindrical bearing holder 4B is formed through the transformer frame 4A, and a rotary shaft 14 is supported in free rotation through bearings 15A and 15B held within the bearing holder 4B.
A flange 16 is engaged to the rotary shaft 14, and a rotor 13B of the rotary transformer 13 is fixed to a lower side of the flange 16. The upper rotary drum 33 is fixed to an upper side of the flange 16. Thus, as a drive motor 6 mounted at a lower edge of the rotary shaft 14 rotates the rotary shaft 14, the rotor 13B of the rotary transformer 13 and the upper rotary drum 33 are rotated.
A head base plate 21 is fastened on the outer circumference of the upper rotary drum 33. The magnetic head 12 is fixed to the upper rotary drum 33 through the head base plate 21. The height of the magnetic head 12 can be finely adjusted with an adjustment screw 22.
Thus, this rotary drum apparatus can record and/or reproduce predetermined video signals on the magnetic tape (not shown) by contacting the outer circumference of the magnetic head 12 through an arrangement to make the magnetic head 12 project outside from a gap between the upper rotary drum 33 and the fixed lower drum 4.